The present invention relates to a photo curable resin composition and more particularly to a photo curable resin composition for use as a permanent mask resist with distinguished pattern formability, heat resistance, adhesibility, mechanical characteristics chemical resistance, electrical characteristics, etc. in the electronic materials such as a solder resist for printed wiring boards, an interlayer insulating film in a high density multilayered board, a solder resist for semiconductor packages, etc. and a photosensitive element using the same.
In the production of printed wiring boards, permanent mask resists have been so far produced by screen printing a heat or ultraviolet ray curing type, resist ink. With the recent trend toward higher integration of electronic devices, more precise wiring patterns and insulation patterns are required in the printed wiring boards, but resist pattern formation by the conventional screen printing has had a difficulty in forming more precise resist patterns owing to generation of exudation, sagging, etc. during the printing. To overcome the difficulty, resist pattern formation by photolithography has been proposed. Specifically, resist patterns are formed by thermocompressing a dry film type, photosensitive resist onto a substrate or curtain or spray coating a liquid photosensitive resist onto a substrate, followed by irradiation of actinic beam such as ultraviolet ray, etc., through a negative type mask and development. The dry film type, photosensitive resist is liable to involve air during the thermocompression onto the substrate to form foams, thereby lowering adhesibility or disturbing the resist pattern, with a fear of lowered resist performance. On the other hand, the liquid photosensitive resist has two types, i.e. solvent developing type and alkali developing type, but the alkali developing type is now dominant from the viewpoints of working environment friendliness and global environment friendliness, as disclosed in JP-A-51-243869 and JP-A-1-141904, where to improve the heat resistance, chemical resistance and electrical characteristics of coating films exposure to ultraviolet ray or heating is further conducted, thereby promoting crosslinking reaction.
However, the conventional liquid photosensitive resist still has problems in practical characteristics such as a humidity-heat resistance and heat resistance. That is, the alkali developing type, liquid photosensitive resist comprises the main component having hydrophilic groups to enable alkali development, and it is presumed that this makes it easy to permeate a chemical solution, water, etc. therethrough, thereby lowering the practical characteristic of resist film.
With the recent trend toward smaller sizes, lighter weight and higher performance of electronic equipment, semiconductor packages of smaller size and higher pin counts are now practically available and their massproduction is in progress. Semiconductor packages such as BGA (ball grid array), CSP (chip size package), etc. particularly require a PCT resistance (resistance to pressure cooker test), which may be called humidity-heat resistance, from the viewpoint of higher reliability. However unfortunately it is in the current situation that the conventional liquid photosensitive resist can withstand such severe conditions only for a few hours to a few tens of hour. Furthermore, with the recent trend toward changing the packaging method from the insert packaging to surface packaging, packaging temperature becomes higher and higher. Specifically, in the case of surface packaging, a cream solder is printed on desired regions in advance, and then the entirety is heated by infrared ray to reflow and set the solder, where the attainable temperature of package inside and outside will be considerably high, for example, 220° to 240° C. Thus, the conventional liquid photosensitive resist has a problem of the so called lowered reflow resistance, for example, generation of cracks on the coating film due to thermal shock or peeling of the coating film from the substrate or sealing material, and thus its improvement has been desired.